Link #47: Spectacular Lights Dance in the Sky at the Earth’s Poles!

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Link #47: Spectacular Lights Dance in the Sky at the Earth’s Poles!

Aurora Borealis
Aurora Borealis by Marcelo Quinan cc2.0

While it may be a little gruesome to read about the sun’s capability to evaporate an organism like the jellyfish, as described in our previous post, that’s not the only thing that the sun can do.

Apart from providing the source of energy for life to flourish on earth, the sun is also capable of making spectacular lights dance in the night sky. That’s right, if you go to either of the earth’s magnetic poles, you’ll see brilliant lights floating and dancing in the night sky. These dancing lights are collectively known as the Northern Lights. Does this make you curious? Read on

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What Are Northern Lights?

Aurora_Borealis_and_Australis_Poster
Images of the aurora australis and aurora borealis from around the world, including those with rarer red and blue lights. By 14jbella cc1.0

Northern Lights are of two types. The ones that occur at the magnetic north pole of earth are known as Aurora Borealis and the ones at the magnetic south pole are referred to as Aurora Australis.

These lights appear in a wide variety of colours in the night sky and seem to float across it. While the most common colours are light or pale green and pink, other colours such as violet, blue, yellow, and red also appear off and on.

In olden times, there were many myths associated with these lights. Different cultures had their own different myths but most were versions of spirits of dead people, ancestors and even animals.

These lights were often seen to be symbols of something greater. For example, the Romans connected them to their Goddess of Dawn, Aurora (thus, the name), while other medieval cultures saw them as harbingers of huge famines or wars.

Most myths related to Northern Lights centre around Aurora Borealis simply because there wasn’t anyone on Antarctica to witness Aurora Australis. Even so, the Maori from New Zealand believe that Northern Lights were a reflection of campfires and torches.


Why Do Northern Lights Occur?

Structure_of_the_magnetosphere
Schematic of magnetosphere. Original bitmap from NASA. SVG rendering by Aaron Kaase. PD image

Northern Lights are such an extraordinary idea that most people wonder about the mechanism behind it. Northern Lights are a result of free electrons and protons colliding with gas molecules inside earth’s atmosphere.

These electrons and protons originate from the Sun and are blown towards earth by the solar wind. Most of these electrons and protons are deflected by the earth’s magnetic field, but they manage to penetrate through at the two poles.

The reason for this is that earth’s magnetic field at the two poles is weaker. Thus, when these electrons and protons penetrate through, they start colliding with various types of gas molecules.


Why Are Northern Lights of Various Colours?

Northern_Lights_Blue
Northern Lights with very rare blue light emitted by nitrogen. Image credit: Varjisakka cc3.0

The colour of Northern Lights varies on the basis of which gas molecules are being hit and also at what heights they are located. The most common colour is light green which is created when these free charged particles collide with oxygen molecules located about 100 kilometres above the earth’s surface.

Similarly, collisions with oxygen molecules located more than 300 kilometres above the earth’s surface create red Northern Lights. Finally, blue Northern Lights are a result of nitrogen molecules colliding with these electrons and protons.




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Sources:

http://en.wikipedia.org/wiki/Aurora
http://geo.phys.uit.no/articl/nord_eng.html
http://www.northernlightscentre.ca/northernlights.html

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